Sucross forms a plaque mainly composed of insoluble glucan on the surfaces of teeth in an oral cavity by the action of Streptococcus mutans (hereinafter, is referred to as S. mutans) which is a cariogenic microbe and then dental caries are produced by the action of acids formed heavily in the plaque.
With the progress of investigations on plaques, it has recently been found that S. mutans be a most principal microbe for causing enamel dental caries. This microbe has a transferase of glucose, which is called "glucosyltransferase", by the action of which glucose of sucrose is cut from fructose and more than scores of thousands of glucoses are bonded with each other to form a polyglucan. Among these polyglucans, the polyglucan which takes part in the occurrence of dental caries is a water-insoluble polyglucan having an .alpha.-1,6 bond and an .alpha.-1,3 bond and hence the polyglucan is called "insoluble glucan". The insoluble glucan is sticky and accumulates the cells of S. mutans on the surfaces of teeth to form cariogenic plaque. If fermentable sugars come into contact with the plaque, they are quickly decomposed into acids to reduce the pH in the plaque below the enamel delimable pH. Furthermore, the plaque containing the insoluble glucan intercepts the buffering, neutralizing, and cleaning actions of salvia, etc. As described above, the formation of the insoluble glucan is a most serious factor for the cariogenic activity of S. mutans. (See, Tadashi Ikeda; "Shikai Tenbo", 49, 684 (1977), R. J. Gibbons and R. J. Fitzgerald; "J. Bacteriol.", 98, 341-346 (1969), T. Ikeda; "Archs oral Biol.", 18, 555 (1973), and I. L. Skklair; "Archs oral Biol.", 19, 199 (1974)).
That is, it is considered that dental caries occur only by the existence of a plaque and also sucrose is a highest-cariogenic material. However, sucrose is an easy-digestible source of calories as well as is an indispensable food for providing abundance and tastefulness to a dietary life. Therefore, it has keenly been desired to prevent the occurrence of the cariogenic action of sucrose, which is the defect of sucrose, but it has not yet been successful to meet the desirement.
Palatinose is a disacharide having the following structural formula and the crystal thereof has 1 mole of water of crystallization. Palatinose has a specific rotation [.alpha.].sub.D.sup.20 of 97.2 (C=1), a melting point of 122.degree.-123.degree. C., a reducing power of 52% of that of glucose, a solubility in water of 46 g/100 g-solution at 40.degree. C. a viscosity of about 90% of that of sucrose and a sweetness of about 42% of that of sucrose and is used as an easy-digestible source of calorie as sucrose but it has never been reported that palatinose is produced as a sweetner. ##STR1##